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Nerve tissue Microscopic structure – practice 2012 Nerve tissue - morphology cells : 1.neurons and 2.glial cells • extracellular material is extremely reduced replaced by glial branched process • neurons receive stimuli and conduct nerve impulse via their processes • action potential transmission to the next cell through synapses (= intercellular contacts) • extensive vasculature with variable amount of connective tissue both in CNS and PNS • blood-brain barrier in CNS Tissue microscopic structure: cells with processes – integrated communicating network neuron theory – contact junctions among neurons Neurons and neuroglia are cells with processes Neuron, neuroglia, blood vessel N3 – cerebellum,HE • NEURON is structural and functional unit of nerve tissue Nerve tissue microstructure (example 2 – brain ) Glial c. Neuron Perikaryon (soma, cell body) receptor region, integration, trophic centre • nucleus • large, lightly basophilic, with dispersed chromatin, prominent nucleolus • RER • abundant → substance of Nissl - tigroid • Golgi apparatus • only in perikaryon! • cytoskeleton (neurofilaments) • mitochondria • inclusions • lipofuscin, melanin Cytoskeleton • Microtubules – axonal transport (anterograde, retrograde, microtubuleassociated motor proteins used ATP – dynein, kinesin) – shape regulation • Neurofilaments (intermediate filaments in neurons) – resistance against deformations – regulatory process • Microfilaments (aktin) Dendrites receptor region principal recieving site • arborisation (branching) increases receptive area of the cell (100 000 contacts and more) • dendritic spines (site of synapse - postsynaptic membrane, actin microfilaments • neurofilaments (NF-L, NF-M, NF-H), other cytoskeleton units, proteosynthetic apparatus except GA • always non- myelinated Axon conductive region • transmit stimuli in the form of action potential to other neuron or effector cell • 1 neuron has 1 axon • metabolically dependent on perikaryon • Golgi type I neurons – motor neurons of CNS with long axon (up to 1 meter) terminate on skeletal muscle • Golgi type II neurons – short axons • axon hillock, initial segment – site of action potential generation • axonal transport transport vesicles, mitochondria , proteins…by anterograde x growth factor, viruses..by retrograde Synapse effector region, unidirectional transmission of nerve impulse presynaptic (axonal) terminal + postsynaptic (dendritic, somatic, axonal) membrane site of chemical message transmission in response to action potential presynaptic : synaptic vesicles with neurotransmitters, microtubules+kinesin, mitochondria synaptic cleft postsynaptic membrane of effector cell: 1. nerve cell 2. muscle cell 3. secretory cell Neuroglia “connective tissue“ of CNS • provide neurons with structural support and maintain local condition for neuronal function • forming 50% volume of CNS • 10 x more abundant than neurons • histological staining • impregnation by Ag, Au salts, histochemical technics Glia - types – – – – astrocytes oligodendrocytes microglia ependymal cells B44 Brain/ Cerebrum (HE) B45 Brain/Cerebrum LFB, luxol fast blue, myelin staining B46 Small brain, cerebellum HE N3 - cerebellum HE • Purkyňova buňka • Granulární neuron Spinal cord / cross section - B48 B48 Spinal cord HE Ependym • epitheloid arrangement of ependymal cells • neural tube neuropithelium remnant B49 Autonomic ganglion B50 Peripheral nerve Peripheral nerve Astrocytes (protoplasmic, fibrous) • • the largest of neuroglia astrocytic end feet- connection to vessels and neurons providing movement of wastes and metabolites to and from neuron • regulate ionic concentration in intercellular space • contribute to blood-brain barrier (together with tight junctions of endothelal cells) mechanical support of neurons proliferation - glial scar glial fibrillary acidic protein Oligodendrocytes • smaller, ↓intermediate fibres, darker nucleus • formation of myelin sheath • myelinisation of several axons Microglia • the smallest, dark elongated nucleus • they migrate to the sites of dead cells, proliferate, phagocytes (dead cells, cell debris…) • mesoderm -derived Ependym • epiteloid arrengement uspořádání – remnant of neuroepithelium of neural tube * secretory elements (cerebrospinal fluid) component of choroid plexus of brain ventricles and central canal of spinal cord Nerve fibres • axons provided by special connective tissue capsules of ectodermal origin • axons: – unmyelinated – myelinated Unmyelinated nerve fibres Myelinated nerve fibres • in PNS: axons are invaginated into cytoplasm of enveloping Schwann cell (sheath is formed by layers of modified cell membranes) x in CNS: cell process of oligondrocytes form sheath • nodes of Ranvier and internode, 1-2 mm • Schmidt-Lanterman´s incisures Myelinated nerve fibres Eg 13 - Myelinizovaný axon N8 – Ganglion HE Satelite cells Neuron Arrangement of nerve tissue in the body, CNS and PNS • CNS • clusters of neurons – cell body: layers, columns (grey matter) • bundles of axons: tracts, fasciculi, lemnisci (white matter) • (grey and white matter differentiation: according to the content of myelin) • PNS • clusters of neurons: ganglia • bundles of axons: cranial spinal peripheral nerves